Fist you have to get the blue viser from van its the medum level hat that restores stamina, then you go to the mine with some grasses and eat one to get some stamina then put the visor on and you can use you hoe or hammer as much as you want and you wount faint so you can get as much money as you want but it gets boring, if you fall one level in the bigger mines you have to eat another grass to get more stamina you only lose stamina if you fall down a hole
hope it helps it helped me alot exspecailly in the fourth mine